1. Field of the Invention
The present invention relates to an engine compartment structure of a vehicle for introducing cool air into an intake air system of the engine.
2. Description of the Related Art
Recently, it has been required to supply a large amount of oxygen to engine combustion chambers as higher power performance is required for automotive engines. However, intake air in an engine is heated in the engine compartment and the temperature of the air rises before the air is sucked into the combustion chambers. When the temperature of the intake air introduced into the chambers rises, the air density is reduced, the weight of the oxygen in the intake air is reduced, and the air filling efficiency of the chambers is also reduced. Thus, the engine power is reduced and engine knocking occurs.
FIG. 11A is a plan view showing an engine compartment structure of a vehicle for introducing cool air into an intake air system of the engine according to prior art and FIG. 11B is an enlarged view showing one of cooling fans mounted on a radiator shown in FIG. 11A. In FIG. 11A, an air intake port 2 of a combustion engine 1 is located behind a first headlamp 3 in the engine compartment. Two cooling fans 5 are mounted on a rear side of a radiator 4, and the cooling fans rotate counterclockwise when they are seen from the engine side. The intake air flowing into the air intake port 2 is sucked into combustion chambers of the engine 1 via an intake duct 6, an air cleaner 7, an intake pipe 8, a surge tank 9 and an intake manifold 10, in that order. A transmission 11 is provided on the right side of the engine 1 when it is seen from a front side of the vehicle. Above the transmission 11, there is a space, as the height of the transmission 11 is lower than that of the engine block 1. The radiator 4 is covered with an under cover 12. In such an engine compartment structure for introducing cool air into the intake air system of the engine as explained above, fresh air FA flows into the engine compartment from outside after passing through a space behind a second headlamp 3a located opposite to the first headlamp 3. On the other hand, heated air HA after passing through the radiator cooling fans 5 turns around toward the air intake port 2, which raises the temperature of the intake air. This results in reduced air filling efficiency to the combustion chambers of the engine.
As an invention to solve the above problem, a structure that restricts temperature increases of the air introduced into an intake air system of an engine is disclosed in Japanese Unexamined Patent Publication No. 5-1634. According to the structure, the temperature of the air introduced into the intake air system from outside decreases, so that the air filling efficiency to the combustion chambers of the engine can be improved. To accomplish this, a baffle plate is provided in the structure in such a way as to extend a fan shroud of a radiator toward the rear of a car body and to intentionally open an air intake port of an intake duct toward the opposite side of the radiator, thereby preventing heated back wind passing through the radiator cooling fans from being introduced into the intake air system of the engine.
However, according to the engine compartment structure for a vehicle that restricts temperature increases of the air introduced into the intake air system of the engine disclosed in Japanese Unexamined Patent Publication No. 5-1634, a baffle plate must be provided, therefore additional expenses for the baffle plate and for the man hours for assembling the baffle plate are required.